1. Field of the Invention
The invention relates to a magnetooptic recording medium for recording and reproducing information by using a laser beam and to a storing apparatus. More particularly, the invention relates to a magnetooptic recording medium for reproducing a recording mark smaller than a laser beam by a magnetically induced super resolution and to a storing apparatus.
2. Description of the Related Arts
In recent years, as an external recording medium of a computer, an optical disk has been highlighted. According to the optical disk by forming recording pits on the submicron order onto a medium by using a laser beam, a recording capacity can be remarkably increased as compared with that of a floppy disk as a conventional external recording medium. When considering a magnetooptic disk of 3.5 inches, although the initial disk has only a capacity of 128 MB, the disk having a capacity of 1.3 GB has been realized in recent years. A magnetooptic disk of 3.5 inches having the largest capacity of 1.3 GB at present will now be described. High density recording is realized by setting a track pitch to 0.90 μm and setting a mark length to 0.38 μm and, further, by using a super resolution technique called MSR (Magnetically Induced Super Resolution). According to the MSR technique, by devising the medium side, a mark smaller than a spot diameter of the laser beam can be recorded and reproduced. By using the MSR technique, the capacity which is 10 times as large as the capacity of 128 MB of the initial disk can be realized.
The MSR technique will now be described. FIGS. 1A and 1B are diagrams showing a reproducing principle of the MSR technique. As for a medium construction, a 3-layer construction of a recording layer 200, an intermediate layer 202, and a reproducing layer 204 will be described as an example. A mark recorded in the recording layer 200 is influenced in a low temperature portion in front of a laser beam 205 by a reproducing magnetic field, so that a front mask 206 is formed in the erasing direction. An arrow 216 indicates a medium rotating direction. In a portion behind the laser beam 205, heat generated by a reproducing power is accumulated, so that a temperature rises, a magnetization of the intermediate layer 202 is extinguished, and a rear mask 212 which faces a same recording direction 210 as that of a reproducing magnetic field 208 is formed in the reproducing layer 204. An aperture 214 is formed in an intermediate portion between the front mask 206 and rear mask 212. Only in this portion, a magnetization in the recording layer 200 is reflected to the reproducing layer 204 through the intermediate layer 202, so that the reproduction by the MSR is realized. The reproduction of the mark smaller than the laser beam 205 can be realized. The MSR technique is particularly a type called a super resolution (MSR) of the double mask type rear aperture detection system.
In case of reproducing by the MSR, it is necessary to raise the reproducing power to a power larger than that in case of the ordinary reproduction and raise a temperature of the reproducing portion. However, usually, since an ID area between data areas is formed by a pit train, there is no need to raise the reproducing power. If the reproducing power is large, a reproduction signal which is inputted to a reproducing circuit is too large and there is a possibility that it exceeds a dynamic range. It is impossible to make the reproducing power coincide with that of the MSR. Therefore, at the head of the data area where the reproduction of the MSR is executed, since the reproducing power at the time of reproducing the ID area is small, a preheating effect is not obtained and the larger reproducing power is necessary. There is, consequently, a problem such that a reproducing power margin is reduced.